Moov Atom (Faststart) option when exporting in H.264

So I recently stumbled into a bit of a rabbit hole around the moov atom in .mp4 files, basically a piece of metadata at the container level that tells the browser how to play the video.

I export all my videos using Adobe Media Encoder (not sure which version but i believe 2025 non beta), then upload them to BunnyCDN to use as direct .mp4 links for autoplaying videos on my Framer site. But I noticed that some videos, especially longer ones, just wouldn’t autoplay properly in Safari, while working fine in Chrome and Firefox.

After digging into it (and talking to Bunny), it turns out the moov atom needs to be at the start of the file for proper streaming and playback. Safari especially doesn’t like it when it's placed at the end, which, apparently, Media Encoder sometimes does without any way of changing it.

This is especially important for, as I understand it:

• Autoplaying background/autoplaying videos on websites (like I’m building in Framer). Even though most videos of mine work, i suspect more than this one has the moov atom at the end, and they would probably load faster.

• Safari, which is less forgiving and more prone to stalling

• YouTube and other platforms that recommend faststart-optimized uploads

• CDNs like Bunny.net, which optimize delivery around moov-at-start files (Their support said this directly to me)
  
  

I fixed it using FFmpeg and the -movflags +faststart command, which moves the moov atom to the beginning of the file without re‑encoding. That solved the problem.

But honestly, this feels like something that should be built into Media Encoder. Either as a default for H.264 exports or at least a visible checkbox somewhere. Right now, there’s no way to control it.

What’s more confusing is I found this old community post, where an Adobe dev said:

“Yes I can confirm that we always place MOOV atom at the beginning of the file (right after FTYP atom) when exporting to H.264 in MP4.”

But the video I just fixed was exported with Media Encoder and still had the moov atom at the end, causing all the playback issues in Safari.

Would love to see Adobe bring this back (or make it actually reliable).